1. Field of the Invention
The present invention relates to high-frequency modules and mobile communication apparatuses including high-frequency modules, and more particularly, to a high-frequency module which can be shared by three different communication systems and a mobile communication apparatus including such a high-frequency module.
2. Description of the Related Art
A triple-band portable telephone has been proposed which can operate in a plurality of frequency bands, such as those in a digital cellular system (DCS) using the 1.8 GHz band, a personal communication service (PCS) using the 1.9 GHz band, and a global system for mobile communications (GSM) using the 900 MHz, as a mobile communication apparatus.
FIG. 12 is a block diagram of a front-end section of a general triple-band portable telephone. FIG. 12 shows a case in which first to third communication systems having frequencies that are different from each other are set to the DCS using the 1.8 GHz, the PCS using the 1.9 GHz, and the GSM using the 900 MHz.
The front-end section of the triple-band portable telephone is provided with an antenna 1, a diplexer 2, first to third high-frequency switches 3a to 3c, first and second LC filters 4a and 4b, and first to third SAW filters 5a to 5c. The diplexer 2 couples a transmission signal sent from one of the DCS, the PCS, and the GSM with the antenna 1 during transmission, and distributes a receiving signal sent from the antenna 1 to one of the DCS, the PCS, and the GSM during receiving. The first high-frequency switch 3a switches between the transmission-section side of the DCS and the PCS, and the receiving-section side of the DCS and the PCS. The second high-frequency switch 3b switches between the receiving section Rxd side of the DCS and the receiving section Rxp side of the PCS. The third high-frequency switch 3c switches between the transmission-section Txg side and the receiving section Rxg side of the GSM. The first LC filter 4a passes transmission signals for the DCS and the PCS and attenuates the harmonics of the transmission signals. The second LC filter 4b passes a transmission signal for the GSM and attenuates the harmonics of the transmission signal. The first SAW filter 5a passes a receiving signal for the DCS and attenuates the harmonics of the receiving signal. The second SAW filter 5b passes a receiving signal for the PCS and attenuates the harmonics of the receiving signal. The third SAW filter 5c passes a receiving signal for the GSM and attenuates the harmonics of the receiving signal.
The operation of the triple-band portable telephone will be described for the DCS first. During transmission, the first high-frequency switch 3a turns on the transmission section Txdp side to send a transmission signal that was sent from the transmission section Txdp and that has passed through the first LC filter 4a, to the diplexer 2, the diplexer 2 performs coupling, and then the signal is sent from the antenna 1. During receiving, a receiving signal received by the antenna 1 is distributed by the diplexer 2, the receiving signal sent from the antenna 1 is sent to the first switch 3a, which is located on the DCS and PCS side, the first high-frequency switch 3a turns on the receiving section side to send the signal to the second high-frequency switch 3b, and the second high-frequency switch 3b turns on the receiving section Rxd side of the DCS to send the signal to the receiving section Rxd of the DCS through the first SAW filter 5a. A similar operation is also performed for transmission and receiving for the PCS.
A case in which the GSM is used will be described next. During transmission, the third high-frequency switch 3c turns on the transmission section Txg side to send a transmission signal which was sent from the transmission section Txg and has passed the second LC filter 4b, to the diplexer 2, the diplexer 2 performs coupling, and the signal is sent from the antenna 1. During receiving, a receiving signal received by the antenna 1 is distributed by the diplexer 2, the receiving signal sent from the antenna 1 is sent to the third high-frequency switch 3c, and the third high-frequency switch 3c turns on the receiving section Rxg side to send the signal to the receiving section Rxg of the GSM through the third SAW filter 5c. 
Since the triple-band portable telephone, which is one of the conventional mobile communication apparatuses, uses three high-frequency switches, at least six diodes constituting the high-frequency switches are required. As a result, the triple-band portable telephone uses a very large amount of power, and a battery mounted to the triple-band portable telephone can be used only for a short period. Also, the operation of each diode is controlled in many operation modes, and thus, a complicated circuit is required.